Porous membranes preparation

Poly(aryl ether ketone)s show outstanding chemical resistance and thermal properries. They are virtually insoluble in all conunon solvents at room temperature. These properties make poly(aryl ether ketone)s attractive materials for porous membrane preparation. 

Table 2.3 Typical porous membranes prepared by the sol-gel route... 

Symmetric porous membranes prepared by sintering, track-etching and leaching techniques... 

Fig. 13. Phase diagram showing the composition pathway traveled by a casting solution during the preparation of porous membranes by solvent evaporation. A, initial casting solution B, point of precipitation and C, point of soHdification. See text.

Porous membranes with selective permeabiUty to organic solvents have been prepared by the extraction of latex films prepared with moderate ratios of PVA—PVAc graft copolymer fractions. The extracted films are made up of a composite of spherical cells of PVA, PVAc microgel, and PVA—PVAc graft copolymers (113). 

Pores Even porous membranes can give very high selectivity. Molecular sieve membranes exist that give excellent separation factors for gases. Their commercial scale preparation is a formidable obstacle. At the other extreme, UF,3 separations use Knudsen flow barriers, with aveiy low separation factor. Microfiltration (MF) and iiltrafiltra-tion (UF) membranes are clearly porous, their pores ranging in size from 3 nm to 3 [Lm. Nanofiltration (NF) meiTibranes have smaller pores. 

Another possibility of constructing a chiral membrane system is to prepare a solution of the chiral selector which is retained between two porous membranes, acting as an enantioselective liquid carrier for the transport of one of the enantiomers from the feed solution of the racemate to the receiving side (Fig. 1-5). This system is often referred to as membrane-assisted separation. The selector should not be soluble in the solvent used for the elution of the enantiomers, whose transport is driven by a gradient in concentration or pH between the feed and receiving phases. As a drawback common to all these systems, it should be mentioned that the transport of one enantiomer usually decreases when the enantiomer ratio in the permeate diminishes. Nevertheless, this can be overcome by designing a system where two opposite selectors are used to transport the two enantiomers of a racemic solution simultaneously, as it was already applied in W-tube experiments [171]. 

Porous membranes have been prepared by leaching an additive from films and tubes of PCL (64,72). The procedure involves extrusion or casting blends of PCL and Pluronic F68, the latter being an FDA-approved oxyethylene-co-oxypropylene triblock copolymer. Treatment of the phase-separated blend with aqueous acetone or aqueous alcohols causes both swelling of the polymer and extraction of the Pluronic F68. The induced pore size and void volume may be controlled by the time, temperature, and solvent composition. 

Liang Z, Susha AS, Yu A, Caruso F (2002). Nanotubes prepared by layer-by-layer coating of porous membrane templates. Adv. Mater. 14 1849-1853. 

Of particular interest are membranes prepared of an inert porous support carrying natural or artificial lipids. These coatings may comprise a single component, such as isopropylmyristate or dodecanol [99, 106], or mixtures of comparable composition as the stratum corneum intercellular bilayer [107, 108], Usually, synthetic lipids are used, due to an elaborate isolation procedure for stratum corneum lipids, with limited yield and the necessity of separation of triglycerides, originating from subcutaneous fatty tissue or skin care products [109],... 

Porous glass membranes prepared by leaching methods can be obtained with pore size between 2 and 200 nm. The internal surface is active and can be... 

Besides the synthesis methods for porous membranes and their modification methods discussed above, other synthesis methods have been reported. These are outlined below. Preparation of dense membranes is discussed in Section 2.2. The other types are the so-called dynamically formed membranes which... 

Suzuki, F., K. Onozato and Y. Kurokawa. 1987. Gas permeability of a porous alumina membrane prepared by the sol-gel process. J. Non-Cryst. Solids 94 160-62. 

Transition-metal nanopartides are of fundamental interest and technological importance because of their applications to catalysis [22,104-107]. Synthetic routes to metal nanopartides include evaporation and condensation, and chemical or electrochemical reduction of metal salts in the presence of stabilizers [104,105,108-110]. The purpose of the stabilizers, which include polymers, ligands, and surfactants, is to control particle size and prevent agglomeration. However, stabilizers also passivate cluster surfaces. For some applications, such as catalysis, it is desirable to prepare small, stable, but not-fully-passivated, particles so that substrates can access the encapsulated clusters. Another promising method for preparing clusters and colloids involves the use of templates, such as reverse micelles [111,112] and porous membranes [106,113,114]. However, even this approach results in at least partial passivation and mass transfer limitations unless the template is removed. Unfortunately, removal of the template may re-... 

Considerable activity has been generated on composite reverse osmosis membranes by Japanese researchers. Patent applications were recently published, for example, covering research at Teijin Ltd. on interfacially formed membranes prepared from polydiallylamines (17) and from amine adducts of trls-(glycidyl) isocyanurate (18). Both types of membranes were formed on micro-porous polysulfone supports. Kurihara and coworkers have developed a composite membrane, designated PEC-1000, which is formed by an... 

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